What Every One Should Know About Paleontology

After a question was posed on the Dinosaur Mailing List regarding the basic information the general public needs to know about paleontology, Dr. Tom Holtz replied with a comprehensive breakdown of what the science has taught us about the history of life on Earth. It has been cross posted on other blogs today, including Superoceras, Archosaur Musings, and SV-POW (UPDATED: Project Drypto, Crurotarsi, RMDRC Paleo Lab, too). Please be sure to click on the link of your choice to read the entirety of Dr. Holtz's piece. I'm not going to include it all here, but I would like to share my perspective on the subject.

When Dr. Holtz's email came through, I was working on a design project on my sofa, facing the south window of our living room. The window looks out on a small dogwood tree that holds a bird feeder - one of the those long tubes full of nyjer thistle seed. A suet cage is sequestered on a shepherd's hook, necessary to keep the squirrels from hogging the scrumptious blocks of fat-encased seeds all for themselves. Naturally, once Dr. Holtz reached the Mesozoic era, covered the evolution of dinosaurs, mammals, and flowering plants. It was impossible not to notice the resonance of the email with what I was watching: all players in the scene before me were members of lineages who began in the Mesozoic. Finch, squirrel, and dogwood: all important parts of the little ecosystem of my yard, all reminders of a heritage stretching back tens of millions of years or more.

Charles Darwin didn't invent the idea of evolution. But his mechanisms of natural and sexual selection were what forced us as a species to take an honest look at our place in nature. It hasn't been an easy understanding to grapple with - we're still arguing over it, after all. Though the opponents of evolutionary education grasp at more and more desperate ways to undermine it, the evidence has piled up to the extent that the absurdity of their arguments is plain to any reasonable person. I'm like plenty of other people: I whine and moan at the state of science education in my home country. The fact that emotion can persuade so much more easily than logical arguments can be discouraging. But the fact is that the scientific story of life on Earth can create an emotional connection, too. I've felt it. Others have felt it. And that's a hopeful thought.


Photo by Stu the Limey, via Flickr.

Evolution Made Us All

Evolution Made Us All from Ben Hillman on Vimeo.

So delightful when the T. rex pops in!

H/T Boing Boing.

A Mosasaur's Tail

If you're ever on the game show Jeopardy and your Daily Double requires you to identify an anguilliform swimmer, you would do well to answer, "What is an eel, Alex?". Eels, with their broad, ribbon-like tails, get around by undulating most of their body. During the Mesozoic, a very different group of animals navigated the seas in a similar fashion: many of the aquatic lizards called mosasaurs.

A new study of a remarkably complete specimen of the mosasaur Platecarpus tympaniticus has found that it employed a different form of locomotion. An international team of researchers led by Johan Lindgren of Lund University has published a paper at PLoS ONE about the specimen called LACM 128319, which preserves much of its skeleton, scale impressions, and even traces of its internal organs and retina.

By comparing the measurements of its caudal vertebrae, Lindgren et al. determined that the tail of Platecarpus was hypocercal, meaning that it was divided in two lobes with a longer lower half. Platecarpus' tail identifies it as a carangiform swimmer, meaning that much less of its body would have flexed to provide propulsion. This has important implications for the kind of hunter it would have been: anguilliform swimmers like eels are very flexible, but it comes at the expense of speed. The fastest swimmers, like tuna, employ what's called thunniform locomotion: their bodies are very stiff, with only their big, crescent-shaped tail fins moving to provide propulsion. Platecarpus existed in the middle of this spectrum, so it was probably a relatively fast swimmer, the better to catch the fish it fed on. Also adding to its speed, its scales were smaller than the most primitive mosasaurs, a feature which stiffened its body and decreased drag.


New restoration of Platecarpus by Dimitri Bodanov, showing hypocercal tail fin. From wikimedia commons.

The member of the mosasaur family that exhibits the most refined traits for living in the water, the 40 foot giant Plotosaurus, was also a carangiform swimmer. Its scales, also known from fossil impressions, were even smaller than those of Platecarpus. Living in the middle of the mosasaurs' span on Earth and tens of millions of years before Plotosaurus, Platecarpus can be considered yet another "transitional" form to tuck in your back pocket for those times when you're called upon to defend the honor of evolution.

Without applying the outdated "ladder of progress" model to evolution, it is fair to say that evolutionary lines can have a progressive "arc" as time goes on. It makes sense that when competition for resources is stiff, bodies respond by adapting for greater efficiency. Using what they observed in Platecarpus, Lindberg et al. compared mosasaurs to other lines of secondarily aquatic animals, including cetacean mammals, marine crocodiles, and icthyosaurs. They found that the basic streamlined body plan, flipper-like limbs, and carangiform locomotion evolved consistently within the first ten million years after these groups' first appearance in the fossil record. Living in water places unique constraints on vertebrate's bodies, and it makes a lot of sense that similar body plans would evolve independently in different animals. There's just no better way to make a living as a big marine predator

If you're interested in the mesozoic sea monsters, one of the most comprehensive resources is Mike Everhart's Oceans of Kansas website. It includes an 1899 description of a Platecarpus fossil written by Charles Sternberg, a collector who got his start working for Edward Drinker Cope.

One last thing: If Sue, Leonardo, and Lyuba deserve cute nicknames, LACM 128319 is equally deserving. But I haven't come across one. Any brilliant ideas?